FIG. 1 is a schematic configuration diagram showing a cross section of a conventional transmitting screen that is generally used in a rear projection type television. In FIG. 1, reference numeral 1 indicates a lenticular lens sheet, and reference numeral 2 indicates a Fresnel lens sheet. Usually, the Fresnel lens sheet 2 and the lenticular lens sheet 1 are placed being adjacent to each other, thereby configuring the transmitting screen. In general, the Fresnel lens sheet 2 is made of a sheet whose light outgoing surface is provided with a Fresnel lens comprising lenses arranged with fine pitches, equally spaced in a form of concentric circles (see Japanese Patent Laid-Open publication No. 59-69748).
As shown in FIG. 1, on the lenticular lens sheet 1, hog-backed lenses are placed on the side of light incidence plane, in such a manner as evenly spaced apart from each other. Outgoing parallel light or convergence light from the Fresnel lens sheet 2 is largely diffused horizontally by the lenticular lens sheet 1, thereby enabling observation of an image in a wide viewing range in the horizontal direction.
In the lenticular lens sheet 1 as described above, as shown in FIG. 1, contrast in a bright room is improved, by providing a shading pattern comprising a layer of light absorption material such as black ink, on a part other than a portion where lights are converged by each lens that are provided on the light incidence plane side.
In the Fresnel lens sheet, for the purpose restricting a stray light or the like so as to expand the range where image observation is possible not only horizontally but also vertically, it has been performed that a diffusion material is mixed inside, a vertical lenticular lens as disclosed in the Japanese Patent Laid-Open Publication No. 60-263932, or a prism shape as disclosed in the Japanese Patent Laid-Open Publication No. 11-271884 are provided on the incidence plane. In addition, in order to restrict speckles of image light (fine variations in brightness, and dazzling), there has been disclosed, in the Japanese Patent Laid-open Publication No. 8-313865, a method to increase Haze (to intensify diffusivity) of the Fresnel lens sheet. Japanese Patent Laid-Open Publication No. 2000-275738 discloses a technique to define a particular range as diffusion characteristics of the Fresnel lens sheet.
Conventionally, in giving diffusion characteristics to the Fresnel lens sheet, there have been problems including the following:
1) it is possible to consider that the diffusion characteristics are obtained by forming vertical diffusive lenticular lens and prism lines with even pitches on the incidence plane of the Fresnel lens sheet. However, there has been a problem that moire may occur with the Fresnel lens and the lenticular lens;
when a general diffusing material is used for giving the diffusivity,
2) the diffusing material itself may cause generation of speckles;
3) since the diffusion characteristics show a tailing pattern (relatively small in a medium angle region and relatively large in a high angle region), a tailing component (scattered light in the high angle region) among transmitted light that has passed through the Fresnel lens sheet, is cut off by the light shielding pattern portion of the lenticular lens, thereby causing a loss in light quantity;
4) ghosts such as double image are formed due to the light path as shown in FIG. 2, but in the diffusion by a conventional diffusing material, such ghosts have not been able to be reduced sufficiently; and
5) since a diffusing agent is expensive, it has been disadvantageous in cost wise.
The present invention has been made to solve the above problems and the object thereof is to provide a Fresnel lens sheet which is bright due to a small light quantity loss, restricted in speckles, does not produce moire, restricted in ghosts, and in addition, it is inexpensive.